It has already been proposed to withdraw petroleum from a well when the pressure from below is no longer sufficient to lift the petroleum to the surface by itself, by using a device which introduces a lifting gas under pressure to a location below the surface of the petroleum in the subterranean deposit and thereby cause the petroleum to move upwardly along a string or casing. The lifting gas may be introduced under pressure continuously or intermittently at various levels along the string so that, at each such level, there is an elevating effect.
It is also known to provide a device for spraying the petroleum concurrently with the lifting thereof by the use of ejectors operating with venturi principles.
Both of these devices have the disadvantage that they require high working pressure and a high consumption of the lifting gas. When the petroleum is lifted in the form of slugs, i.e. units of the liquid moved as a mass, the slugs of petroleum alternate with the slugs of gas and there may occur a downward slippage of the crude oil along the inner wall of the casing reducing the quantity of oil withdrawn and leading to increased gas consumption.
There is still another known device using the Coanda effect. This device operates by means of pumping the lift gas through an annular space, previously sealed with a packer over the orifices. The gas is introduced into the string or casing at different levels through annular slots having adjustable openings. Above these slots there is formed a venturi nozzle allowing the fluid jet to deflect along the inner walls of the nozzle due to the Coanda effect and the active upward entrainment of the petroleum, concurrently with the dispersal of the slugs by their homogenization with the lifting gas.
The disadvantage of this particular device is its low efficiency, unsteady operation and great consumption of lift gases.